The present invention relates to screen editing for a video printer, and more particularly to a screen editing method which does not damage the contents of screens to be edited when forming an edited screen.
FIG. 1 shows a block diagram of a conventional video printer. The video printer in FIG. 1 receives two screens of data and stores them into respective memories to selectively output each. When printing two screens, the video printer solves the inconvenience of sequentially inputting and printing the data of each screen.
The video printer of FIG. 1 stores or outputs screen information by fields. An input video signal is a digitized analog signal suitable for storing the screen information into a memory. The memory for storing the screen information has a sufficient capacity for storing fields of screen information. For instance, given that the number of vertical samplings of a screen is M, the number of horizontal samplings is N, and the resolution per sampled pixel is Q bits, the minimum capacity of the memory becomes Q.times.M.times.N bits. In order to store two screens worth of data, two memories each having the minimum memory capacity, or one memory having twice the minimum memory capacity may be used. In FIG. 1, two memories having the minimum memory capacity are used and have the same memory regions (same addresses).
Input screen information is distributed to memories 120 and 130 according to an input selection signal SELECT.sub.-- IN as well as a memory read/write signal R/W from a controller 150 and an address signal ADDR from an address generator 140. For example, when the input screen information is written into first memory 120, controller 150 controls input selection signal SELECT.sub.-- IN so that an input selection switch 110 selects the path to first memory 120, and sets memory read/write signal R/W so as to establish a write mode. Controller 150 also applies an address generating signal ADDR.sub.-- GEN to address generator 140 which in turn starts to operate. Address signal ADDR generated from address generator 140 is then supplied to first memory 120 to designate an address where the screen information via input selection switch 110 is to be written.
The screen information written in memories 120 and 130 is selectively output to an unshown thermal print head (TPH) and is printed according to an output selection signal SELECT.sub.-- OUT together with memory read/write signal R/W from controller 150 and address signal ADDR from address generator 140. For instance, when the screen information written in first memory 120 is printed, controller 150 controls output selection signal SELECT.sub.-- OUT so that an output selection switch 160 selects the path to first memory 120, and sets memory read/write signal R/W so as to establish a read mode. Controller 150 applies an address generating signal ADDR.sub.-- GEN to address generator 140 which in turn starts to operate. Address signal ADDR generated from address generator 140 is supplied to first memory 120 to designate a read address.
Now, referring to FIG. 2 showing a reading out process of screen information, operation of reading out the screen information written in memories 120 and 130 and supplying the information to the TPH, is described. In FIG. 2, the location of pixels constituting the screen information is indicated by a combination of a row address R and a column address C, and can be represented as coordinates (R,C). Here, the incrementing directions of row address R and column address C are denoted as Y and X, respectively, and the final values of row address R and column address C are Re and Ce. In reading and printing the screen information, pixels of the leftmost column, first, are read out and printed, and then pixels of the column immediately to the right thereof are read out and printed. This process is repeated until pixels of the rightmost column are read out and printed, to complete one screen printing operation. More specifically, in FIG. 2, among pixels constituting screen information, the pixel components of the leftmost column are read out in the order of: (0,0).fwdarw.(1,0).fwdarw.(2,0) . . . .fwdarw. (Re,0); and supplied to a line memory of the TPH so as to be printed. After all the pixels of the leftmost column are read out to be printed, pixels of the column immediately to the right thereof are read out and printed in the order of: (0,1).fwdarw.(1,1).fwdarw.(2,1) . . . .fwdarw. (Re,1). The process is repeated until a final column Ce, which is the completion of one screen printing operation.
The video printer of FIG. 1 is advantageous in the rapid input of screen information and the enhanced processing capacity of a video printer by storing two screens of data, selecting and printing each one individually. However, although the video printer of FIG. 1 can select and output one screen of data to be printed, the video printer has no function to extract part of a screen (subscreen) and insert it into another screen (main screen).
To include the screen editing function, the video printer of FIG. 1 may comprise an additional memory for screen editing. For instance, in the case of extracting part of the second memory and inserting it into the first memory to print it, first, the screen information of the first memory is stored in a separate memory. An extracted region of the second memory is read out and then overwrites a corresponding inserting region of the first memory in the separate memory, so that an edited screen is obtained. Finally, the edited screen is read out from the separate memory and printed. However, such a method needs an additional memory besides the screen editor so that the system becomes more expensive and slows the processing speed.